Monitoring of tracks shaped by material extrusion: determination of the most influential printing parameters on their dimensional accuracy

Although additive manufacturing printers have existed for almost 40 years, they still need improvement to meet the process stability and repeatability required by demanding industrial sectors such as aerospace or automotive. The first step in that purpose is to detect and quantify the occurring deviations. This can be performed with in-situ monitoring, by assessing the influence of the printing parameters on the dimensions and temperature of the deposited tracks. This paper proposes in-situ monitoring using a thermal camera and a profilometer. It was applied to a Material Extrusion printer (Ultimaker 2+) printing tracks in polylactic-acid. A full factorial design was established with three factors (printing temperature, wall flow and printing speed) at two levels. Their influence on the track dimensions (height, width and section) and temperature were monitored. ANOVA was used to check the statistical significance of each factor and interaction, and allowed the creation of polynomial models to fit the experimental data. The observations made with the profilometer and the thermal camera were reliable and allowed to characterize the deposited tracks accurately. Nevertheless, the dispersion observed for each test were high, demonstrating the expected lack of printer repeatability. Finally, indicators based on the concepts of trueness and precision from ISO 5725-1 were established to select the best printing parameters. The recommended parameters found were a printing temperature of 264 °C and a wall flow of 82.5%, with no influence from the printing speed.